Optical tracking systems for tracking the position and orientation of a moving object in a reference coordinate system are known in the art. These tracking devices employ optical detectors (e.g., Charge Coupled Devices) for gathering information about the position and/or orientation of a moving object. One configuration for such an optical tracking device is fixing one or several optical detectors on the moving object and fixing a set of light sources (e.g., Light Emitting Diodes) at a known position in the coordinate system. Another configuration for such an optical tracking device is fixing a set of light sources on the moving object and fixing one or several optical detectors at a known position in the reference coordinate system. Yet another configuration is combining the former configurations and fixing both detectors and light emitters on the moving object and at a known position in the reference coordinate system. Optical tracking systems enable automatic decision making based of the determined position and/or orientation. For example, a pilot may aim at a target by moving only her head toward the target (i.e., the pilot does not have to move the aircraft toward the target). The optical tracking system determines the orientation (i.e., elevation, azimuth and roll) of the helmet, worn by the pilot, in the aircraft coordinate system. As a further example, the optical tracking system may track the movements of a user of a virtual reality system (e.g., a game, a simulator) determining the position of the user.
However, an optical detector placed on the moving object can detect the light emitters in the reference coordinate system only as long as the light emitters are within the Field Of View (FOV) of the detector. Therefore, the FOV of the optical tracking system (i.e., the range of positions in which the optical tracking system tracks the moving object) is limited by the FOV of the optical detector. Similarly, the fixed light detector can track the moving object as long as the light emitters attached to the moving object are within the FOV of the fixed light detector. Thus, the intersection of the FOV of the moving light detector, with the FOV of the fixed light detector, defines the tracking space of the tracking system.
Reference is now made to FIG. 1, which is a schematic illustration of an optical detector, generally referenced 10, which is known in the art. Optical detector 10 includes an optical sensor 12 optically coupled with a lens 14. Lens 14 includes an entrance pupil 16. The FOV φ of optical detector 10 is inversely proportional to the ratio between the focal length f of lens 14 and the size d of optical sensor 12. Furthermore, the accuracy of optical detector 10 is proportional to the angular resolution thereof. Therefore, when the size of sensor 12 (e.g., number of pixels) is fixed, increasing the focal length of lens 14, increases the resolution but decreases the FOV of optical detector 10.
U.S. Pat. No. 3,678,283 issued to LaBaw, and entitled “Radiation Sensitive Optical Tracker”, is directed to a system for determining the sight line of a pilot with respect to a point in a cockpit. The optical tracker includes: two detector assemblies and three light emitters. The first detector assembly is mounted on the helmet of the pilot. The first light emitter is mounted on the helmet of the pilot. The second detector assembly is mounted on the cockpit, at the point. The second and third light emitters are mounted on the cockpit, equally spaced on either side of the bore sight line in front of the pilot.
The detector assemblies include lateral photo detectors able to detect the lateral position of the light spot. The light emitters illuminate at a light frequency corresponding to the maximum sensitivity range of the detectors. The two light emitters mounted on the cockpit illuminate the detector mounted on the helmet. The illuminator mounted on the helmet illuminates the detector mounted on the cockpit. The determination of the azimuth and elevation angles, of the line of sight of the pilot, is irrespective of the helmet position within the cockpit. The amount of roll of the head of the pilot is computed by the output of the helmet mounted detector, which detects the two cockpit mounted light emitters.
U.S. Pat. No. 5,767,524 issued to Barbier et al., and entitled “Optical Device for Determining the Orientation of a Solid Body”, is directed to a system for determining the orientation of a first solid body with respect to a second, solid body. The orientation determination system includes: three sets of optical source/detector. Each optical source/detector set includes an optical source and an optical radiation detector. At least one source/detector set is mounted on the first solid body. At least one source/detector set is mounted on the second solid body. On at least one of the solid bodies there are mounted two source/detector sets.
The orientation system determines in the first referential system, of the first solid body, two straight lines corresponding to the light radiation coming from the second referential system. The orientation system determines in the second referential system, of the second solid body, two straight lines corresponding to the light radiation coming from the first referential system. The knowledge of the orientation of at least two distinct straight lines in each of the referential systems gives, by computation of the rotation matrix, the three parameters of orientation of the first solid body with respect to the referential system of the second solid body.